I've found an API labeled aws-ecomm-customers-who-viewed-x-also-viewed but I can't figure out if it's for any product or only works for products on your own store.
The reason I ask is because, it seems that the Amazon website no longer displays "Customers Also Viewed" for any products at all.
Amazon Personalize trains ML models to provide recommendations based on your data only. These models are private to your AWS environment and do not include data from Amazon.com or any other source outside of what you provide.
https://docs.aws.amazon.com/personalize/latest/dg/how-it-works.html